The present invention relates to an optical dilatometer, including a furnace, in which a sample may be laid on a sample carrier, and an optical system for measuring a length of the sample at different temperatures.
Dilatometers are measuring devices, which measure the linear thermal expansion of a sample as a function of the temperature. An optical dilatometer is known from European Patent Document EP 1 329 687, in which a holder for the sample is situated between two optical systems. The sample is enclosed by a tubular furnace body, so that corresponding temperature changes may act on the sample. For a measurement of the length change, a sample is laid in a furnace and one of the optical systems is pointed at one end of the sample and the other optical system is pointed at the other end of the sample. This orientation of the optical systems and/or the sample is comparatively complex.
The present invention is therefore based on the object of providing a dilatometer which is easy to handle and has a simple construction.
According to an exemplary embodiment of the present invention, a light source and a collimator for generating a parallel beam path are situated on one side of a furnace, and the length of a sample is detectable via a silhouette image by a sensor situated on the diametrically opposite side. The necessity of orienting the optical system or the sample is thus dispensed with, because the sample may be measured at any arbitrary point on the sample carrier.
According to another exemplary embodiment of the present invention, a filter is provided on the receiver side which is only transparent to beams of a specific wavelength, which are emitted on a side of a light source. Interfering influences due to light or beams having another wavelength may thus be precluded relatively reliably.
A telecentric optical system may be situated on the receiver side. The silhouette image of the sample may be imaged on a sensor which may be implemented as a high-speed linear CCD sensor to automatically detect the sample length. For a rapid and simple measurement, the sensor may be connected to an A/D converter, which is connected to a controller for recognizing the boundary of the acquired image.
For especially precise measurement, the light source is formed by a high-power GaN LED, whose light has an especially constant wavelength. A diffuser may also be situated between the light source and the collimator.
To implement a uniform temperature profile, the sample chamber has a cylindrical shape, the sample carrier being situated radially centered in the sample chamber and between a top and bottom heating element. Windows transparent to the beam path are provided on diametrically opposite sides of the sample chamber.
An advantageous construction of the furnace results through a furnace body divided into a top part and a bottom part, the partition plane between the top part and the bottom part passing through the sample chamber between the top and bottom heating elements. As a result, the top part may be removed from the bottom part of the furnace body, because of which the sample chamber is easily accessible. It is also possible to charge the sample changer using robot technology very easily. The furnace body expediently has a cylindrical basic shape, whose axis is coincident with that of the sample chamber. The furnace is designed for operation under vacuum and protective gas. Corresponding precautions such as seal elements at the partition plane and the optical windows guarantee this type of operation.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.